In the absorptive state, what is the primary source of energy for most cells?

During the absorptive state, which occurs shortly after eating when nutrients are being absorbed into the bloodstream, carbohydrates serve as the primary source of energy for most cells in the body. When carbohydrates are consumed, they are broken down into glucose, which quickly enters the bloodstream. This rise in blood glucose levels stimulates the release of insulin, a hormone that facilitates the uptake of glucose into cells.

Cells utilize glucose primarily for producing ATP (adenosine triphosphate), which is the energy currency of the cell. In the absorptive state, insulin also promotes the storage of excess glucose as glycogen in the liver and muscle cells and encourages the synthesis of fat from glucose when glycogen stores are sufficient.

Fats and proteins play important roles in metabolism, but in the immediate postprandial (post-meal) state, the body predominantly relies on carbohydrates for immediate energy needs. Fats are generally metabolized for energy during periods of fasting or prolonged exercise when carbohydrate stores are lower. Meanwhile, proteins are primarily used for building and repairing tissues rather than as a primary energy source. Vitamins do not provide energy themselves; they act as cofactors for various metabolic processes but are not sources of caloric energy.